1. Field of the Invention
The present invention relates to a telescope that displays both an image of an object and a digital reading to an observer, and in particular to a telescope that displays the digital reading in an invariable manner.
2. Description of the Prior Art
A conventional telescope is used to observe an object by forming an image of the object through optical elements that focus the image in front of an ocular system. Example of the optical elements include a right-angle prism, a roof prism, and a Porro prism that focuses the image on an image plane in front of the ocular system. The observer can see the image of object. However, most of the telescopes are modified to add an electronic signal generation system that provides an electronic signal carrying digital data, such as distance and direction of the object that is observed with the telescope. The electronic signal is also processed by optical elements to form an image on the image plane to be read by the user of the telescope. Thus, the user can simultaneously see the images of both the object and the electronic signal through the ocular system.
However, some telescopes are of adjustable magnification, and thus the telescopes include a magnification lens group that is arranged between the image plane and the ocular system for adjusting the magnification of the image of the object. The image of the electronic signal is usually focused on the image plane in front of the magnification lens group and is thus subject to the magnification caused by the magnification lens group. This makes the size of the image of the electronic signal varies and thus imposing an underside limitation to the magnification the object image. Further, brightness of the electronic signal changes with the adjustment of magnification factor, which causes undesired effect to the observer's eyes and digital control of the system.
Hence, a telescope is required to overcome the above-mentioned disadvantages of the prior art.